The present invention is directed to an artificial joint for implantation into the living body.
Different types of artificial or prosthetic joints have been known for some time. The stability of a total joint prosthesis is a compromise between biomechanics of design and integrity of existing biological structures. A constrained prosthetic device, such as one disclosed at M. Post et al, Clin. Orth. and Rel. Res. 144 (1979) p. 135, creates significant forces and pressure within the bone-cement-prosthesis interface with the danger of subsequent loosening or failure of the device itself. A unconstrained prosthetic device, as disclosed at S.A.V. Swanson, J. Biomed. Eng. Vol. 1, p. 253 (1976), has the propensity for dislocation.
Artifical joints dependent on magnetic force intersaction have been attempted before. For example, U.S. Pat. No. 4,024,588 of Janssen et al, issued May 24, 1977, discloses a prosthetic joint of head and socket construction with at least one implanted magnet for fostering mutual rotational and translational movement of these portions about their point of pivoting (column 2, lines 22-26). The magnetic force generated may be either of attraction or repulsion. The patentees have also disclosed their work in this area in Z. Orthop. 133 (1975) pp. 400-401.
The prosthetic joint disclosed in U.S. Pat. No. 4,024,588 has several attendant difficulties in that the magnetic field lines of force pass directly along the axes or direction of motion of the head and socket members. The point of contact between the head and socket members is subjected to increased force which can lead to greater wear generated by the magnetic lines of force. If magnetic force of repulsion is employed, then the joint members can be subject to floating and ultimate dislocation. If magnetic force of attraction between members is utilized, then the artificial joint could be subject to inelastic transmission of shocks along the skeletal structure with propensity for further skeletal injury or joint dislocation too. This, in fact, is a problem even recognized in U.S. Pat. No. 4,024,588 at column 2, lines 29-40.
Accordingly, it is an object of the present invention to provide an artificial joint for insertion into the living body with a minimum of external features or connective arrangements.
It is also an object of the present invention to provide an artificial joint based on magnetic attraction wherein magnetic attraction between joint members acts to maintain the stability and integrity of the artificial joint without interfering with the movement of the joint members.
It is still a further object of the present invention to provide an artificial joint based on magnetic attraction between joint members wherein freedom of movement of joint members closely simulates the natural joint being replaced.
Other objectives of the present invention will be readily apparent from the disclosure herein.